Captain Obvious

This is the Revell 2-in-1 Challenger I did, I think it's a pretty nice kit...

These wheels lok pretty close, but it's a chunk of change to buy a Tamiya kit for the wheels...

I just spray the inside of the tub my chosen main color (usually a flat lacquer), brush paint secondary colors, then just brush paint the portion of the tub that will be visible underneath with flat black, usually the driveshaft tunnel and the area around the firewall.

I've used tint film that I picked up at Walmart (still have a ton left on the roll)...the biggest challenge is to keep from getting air bubbles underneath it.

The rear window of my GTO is tinted with the film, on the inside as it would be on a 1:1...

I keep forgetting to try clear enamel, but I have had some success using Future floor polish for light lenses.  Don't think it's quite strong enough for glass though.

as one applies these lenses, how do you keep the lines parallel to the ground and each other?

I'll assume you mean the molded-in lines on a headlight lens?  I just eyeball it as close as possible when installing them, then rotate as needed with a toothpick or tip of a hobby blade before the adhesive sets.